G-protein coupled receptors (GPCRs) are proteins responsible for transducing a signal within a cell. GPCRs have usually seven transmembrane domains. Upon binding of a ligand to an extra-cellular portion or fragment of a GPCR, a signal is transduced within the cell that results in a change in a biological or physiological property or behaviour of the cell. GPCRs, along with G-proteins and effectors (intracellular enzymes and channels modulated by G-proteins), are the components of a modular signaling system that connects the state of intra-cellular second messengers to extra-cellular inputs.
GPCR genes and gene products can modulate various physiological processes and are potential causative agents of disease. The GPCRs seem to be of critical importance to both the central nervous system and peripheral physiological processes.
The GPCR protein superfamily is represented in five families: Family I, receptors typified by rhodopsin and the beta2-adrenergic receptor and currently represented by over 200 unique member; Family II, the parathyroid hormone/calcitonin/secretin receptor family; Family III, the metabotropic glutamate receptor family, Family IV, the CAMP receptor family, important in the chemotaxis and development of D. discoideum; and Family V, the fungal mating pheromone receptor such as STE2.
G proteins represent a family of heterotrimeric proteins composed of α, β and γ subunits, that bind guanine nucleotides. These proteins are usually linked to cell surface receptors (receptors containing seven transmembrane domains) for signal transduction. Indeed, following ligand binding to the GPCR, a conformational change is transmitted to the G protein, which causes the α-subunit to exchange a bound GDP molecule for a GTP molecule and to dissociate from the βγ-subunits.
The GTP-bound form of the α, β and γ-subunits typically functions as an effector-modulating moiety, leading to the production of second messengers, such as cAMP (e.g. by activation of adenyl cyclase), diacylglycerol or inositol phosphates.
Greater than 20 different types of α-subunits are known in humans. These subunits associate with a small pool of β and γ subunits. Examples of mammalian G proteins include Gi, Go, Gq, Gs and Gt. G proteins are described extensively in Lodish et al., Molecular Cell Biology (Scientific American Books Inc., New York, N.Y., 1995; and also by Downes and Gautam, 1999, The G-Protein Subunit Gene Families. Genomics 62:544-552), the contents of both of which are incorporated herein by reference.
Known and uncharacterized GPCRs currently constitute major targets for drug action and development. There are ongoing efforts to identify new G protein coupled receptors which can be used to screen for new agonists and antagonists having potential prophylactic and therapeutic properties.
More than 300 GPCRs have been cloned to date, excluding the family of olfactory receptors. Mechanistically, approximately 50-60% of all clinically relevant drugs act by modulating the functions of various GPCRs (Cudermann et al., J. Mol. Med., 73:51-63, 1995).
ChemerinR, also called Dez [Sequence ID Nos:1 (human polynucleotide sequence, FIG. 1); 2 (human amino acid sequence, FIG. 2); 3 (mouse polynucleotide sequence, FIG. 3); 4 (mouse amino acid sequence, FIG. 3); 5 (rat polynucleotide sequence; FIG. 4); and 6 (rat amino acid sequence, FIG. 4)] has been described as an orphan G protein coupled receptor related to GPR-1 (38% overall amino acid identity), C3a receptor (38%), C5a anaphylatoxin receptor (36%) and formyl Met-Leu-Phe receptors (35%). ChemerinR is more distantly related to the chemokine receptors subfamily (Methner A, Hermey G, Schinke B, Hermans-Borgmeyer I. (1997) Biochem Biophys Res Commun 233:336-42; Samson M, Edinger A L, Stordeur P, Rucker J, Verhasselt V, Sharron M, Govaerts C, Mollereau C, Vassart G, Doms R W, Parmentier M. (1998) Eur J Immunol 28:1689-700). ChemerinR transcripts were found to be abundant in monocyte-derived dendritic cells and macrophages, with or without treatment with LPS. Low expression can also be detected by reverse transcription-PCR in CD4+ T lymphocytes. In situ hybridization experiments also showed that the receptor was differentially regulated during development, with a prominent expression in developing osseous and cartilaginous tissues. It was also detectable in the adult parathyroid glands, indicating a possible function in phosphocalic metabolism.
The gene encoding ChemerinR was assigned by radiation hybrid mapping to the q21.2-21.3 region of human chromosome 12, outside the gene clusters identified so far for chemoattractant receptors. ChemerinR was tested in fusion assays for potential coreceptor activity by a range of HIV-1, HIV-2 and SIV viral strains. Several SIV strains (SIVmac316, SIVmac239, SIVmacl7E-Fr and SIVsm62A), as well as a primary HIV-1 strain (92UG024-2) efficiently used ChemerinR as a co-receptor. This receptor therefore appears to be a coreceptor for immunodeficiency viruses that does not belong to the chemokine receptor family. It is also a putative chemoattractant receptor and it could play an important role in the recruitment or trafficking of leukocyte cell populations. ChemerinR, by its specific expression in macrophages and immature dendritic cells, appears as a particularly attractive candidate receptor involved in the initiation and early regulation of immune responses.
TIG2 (Tazarotene-induced gene 2, thereafter Preprochemerin [Sequence ID Nos: 7 (human Preprochemerin polynucleotide sequence, FIG. 6); 8 (human amino acid sequence, FIG. 6); 9 (mouse polynucleotide sequence, FIG. 7); and 10 (mouse amino acid sequence, FIG. 7)] was identified as a cDNA, the expression of which is up-regulated by the treatment of skin raft cultures by the retinoic acid receptor (RAR) beta/gamma-selective anti-psoriatic synthetic retinoid, tazarotene [AGN 190168/ethyl 6-[2-(4,4-dimethylthiochroman-6-yl)-ethynyl]nicotinate] (Nagpal S, Patel S, Jacobe H, DiSepio D, Ghosn C, Malhotra M, Teng M, Duvic M, Chandraratna R A. (1997) J Invest Dermatol 109: 91-5). The retinoid-mediated up-regulation in the expression of Preprochemerin was confirmed by Northern blot analysis. The Preprochemerin is located at 17p13.3 position, a region associated with pancretic tumorigenesis. The Preprochemerin cDNA is 830 bp long and encodes a putative protein product of 163 amino acids. Preprochemerin is expressed and induced by tazarotene in culture only when keratinocytes and fibroblasts form a tissue-like 3-dimensional structure. RAR-specific retinoids were also shown to increase Preprochemerin mRNA levels. In contrast, neither RXR-specific retinoids nor 1,25-dihydroxyvitamin D3 increased Preprochemerin levels in these cells. Preprochemerin is also expresssed at high levels in nonlesional psoriatic skin but at lower levels in the psoriatic lesion and its expression is up-regulated in psoriatic lesions after topical application of tazarotene. In addition, Preprochemerin has been shown to be dramatically upregulated by 1,25 dihydroxyvitamin D3 and dexamethasone in osteoclast-supporting stromal cells (Adams A E, Abu-Amer Y, Chappel J, Stueckle S, Ross F P, Teitelbaum S L, Suva L J. (1999) J Cell Biochem 74: 587-95).
Dendritic cells (DCs) and macrophages are professional antigen-presenting cells that play key roles in both innate and adaptive immunity. DCs and macrophages are attracted to infection and inflammatory sites by a variety of factors, among which chemokines constitute the largest group so far (Caux, C. et al. (2002) Transplantation 73: S7-S11, Mellman, I. and Steinman, R M (2001) Cell 106:255-258). It has been shown that tremendous functional, morphological and metabolic diversity exists among these cell populations. One of these functional differences is the expression of differential sets of chemoattractant receptors, which is responsible for the selective recruitment of specific cell subpopulations, according to their lineage, origin and maturation state (Caux, C. et al. (2002) Transplantation 73: S7-S11). Many tumor types have been demonstrated to attract macrophages and DCs through the direct or indirect production of chemoattractant factors (Coussens, L M and Werb, Z. (2002) Nature 420:860-867, Vicari, A P and Caux, C. (2002) Cytokine Growth Factors Rev. 13:143-154). These include a number of CC-chemokines, such as MCP-1.
DCs are specialized antigen-presenting cells located throughout the human body. DCs function as sentinels of the immune system. They serve as essential link between innate and adaptive immune systems and induce both primary and secondary immune responses (Palucka, K A and Banchereau, J. (1999) J. Clin. Immunol. 19:12-25). They traffic from the blood to the tissues where, while immature, they capture antigens. They then leave the tissues and move to the draining lymphoid organs where, coverted into mature DCs, they initiate the immune response by activating naïve CD8+ cells, which seek out and kill the antigen-expressing tumor cells. Chemokines are important effectors of the regulation of DCs recruitment, and depending on the chemokine gradient released at the site of injury, different DC populations will be recruited. It is expected that the type of resulting immune response will likely be dependent on the DC subpopulation recruited and thus on the chemokines secreted (Caux, C. et al. (2002) Transplantation 73: S7-S11).